A new generation of optoelectronic devices, such as organic photovoltaics (OPVs), are fabricated using organic semiconductors as their active components. Organic photovoltaic devices are thin film based semiconductor diodes that convert light into electricity by using semiconducting conjugated polymers as active materials capable of harvesting visible light and generating electrons. They do this by absorbing visible photons and creating an excited state known as an exciton (electron-hole pair bound together). Excitons can be broken into electron-hole pairs and separated into charges by appropriate electric fields.
OPVs emerge as one of the most promising technologies in the field of renewable energy, with attractive features, such as the use of low-cost polymeric materials that are light in weight, flexible, and produced by cost-effective processing methods. There are several known types of polymer-based OPVs, such as single layer, double or multi-layer OPVs, and bulk heterojunction OPVs. The best performing OPVs are blended heterojunction OPVs in which a p-type (hole accepting) polymer is blended with an electron accepting material, such as a fullerene, or inorganic nanocrystal (e.g., semiconductor quantum dot, nanorod or tetrapod).
A drawing illustrating the working principle of a prior art OPV based on p-type (donor) and n-type (acceptor) materials is presented in FIG. 1.
Irrespective of their structure, conventional thin-film based OPVs have a polymer layer of a thickness of at least 100 nm to absorb sufficient light to be able to generate electricity. However, this makes them opaque so that it reduces their utilization in technologies where transparency of the film/device is desired.
Transparent OPVs with very thin active material (50 nm or less) in the form of bulk heterojunctions have been realized, with power conversion efficiency as high as 3% and relatively low transparency, i.e., 75% as reported by Solarmer Energy Inc.
As such, there remains a need for transparent thin-film semiconductor compositions based on conductive polymers and electron acceptor material blends that exhibit efficient and effective charge transfer, charge separation and charge transport, and, at the same time, high transparency, for use in the development of, for example, devices utilizing transparent OPVs and the like.